1. Field of the Invention
The present invention relates to arrangements for driving a member in bidirectional fashion along a linear path, and more particularly to arrangements for reciprocating a shuttle assembly adjacent print paper in a line printer.
2. History of the Prior Art
It is known to provide a line printer in which a shuttle assembly including a hammer bank is driven in reciprocating, bidirectional fashion along a linear path adjacent a platen-supported ribbon and print paper or other printable medium as the individual hammers of the hammer bank are actuated so as to impact the printable medium and effect the desired printing. An example of such an arrangement is provided by U.S. Pat. No. 3,941,051 of Barrus et al, issued Mar. 2, 1976 and commonly assigned with the present application. The arrangement shown in the Barrus et al patent drives the shuttle assembly using a counterbalanced, cam controlled positive drive mechanism. The mechanism has sufficient mass and drive power to maintain substantially constant speed despite the variable braking effect that is introduced during printing and the effect of spring loaded cam follower bearings. The controlling cam surfaces must be precisely generated for the desired trapezoidal velocity function, although substantial wear can have an adverse effect on the nature of the motion. With such an arrangement, a large drive motor and flywheel are desirable for stability, and there are practical limitations on the shuttle rate that can be achieved.
An alternative arrangement which avoids some of the problems present in the system of the Barrus et al. patent and which provides certain other advantages is shown in a co-pending application of Jerry Matula, Ser. No. 765,873, filed Feb. 4, 1977 and commonly assigned with the present application. The printer disclosed in the Matula application drives the shuttle assembly using a linear motor. The linear motor includes a coil coupled for linear movement in conjunction with the shuttle assembly and a surrounding permanent magnet. The coil is bidirectionally energized by a circuit which is sensitive to movement of the shuttle assembly between opposite limits and which energizes the coil in accordance with the difference between the actual and the desired velocity of the shuttle assembly. The coil energizing circuit saturates whenever the actual velocity of the shuttle assembly falls below a minimum value to provide a large driving current to the coil following reversals in direction and at any other time that high energization of the coil may be needed. For the most part, however, resilient stop elements provide substantial rebounding force on change in direction so that servo control may be employed to provide the small amount of energizing current necessary to maintain the shuttle assembly at a nominal velocity.
The linear driving arrangement described in the Matula application provides a relatively simple and direct approach to bidirectional shuttle assembly driving, and functions efficiently and effectively for most applications. However, there may be certain applications where other arrangements would be more advantageous. This is particularly true in situations where the frame of the printer or other structure for supporting the shuttle drive is not capable of resisting the shaking or other vibratory motion which results from the reciprocating movement of the linear motor or where the system is otherwise incapable of tolerating the vibration and shaking which are usually present with a shuttle drive of that type.
Accordingly, it would be desirable to provide alternative arrangements for driving a shuttle assembly which may provide certain advantages such as substantial reduction in the vibration and similar undesired forces or motions.